1. Field of the Invention
This invention pertains generally to treatment of carpal tunnel syndrome, and more particularly to both a method and apparatus for treatment by injection of a biological substance into the flexor retinaculum.
2. Description of Related Art
The carpal tunnel is an area in the hand adjacent the wrist which is formed by an arch of the eight wrist bones, spanned on its palmar surface by the flexor retinaculum. Functionally, the flexor retinaculum acts as a pulley. Passing through the carpal tunnel are nine flexor tendons with their synovial membranes, four lumbrical muscles, and median nerve. Without the flexor retinaculum, the flexor tendons tend to bowstring, losing their ability to preserve their appropriate moment arms, and resulting in a loss in both strength and dexterity to the wrist and hand that the carpal tunnel tendons help control.
Carpal tunnel syndrome (CTS) is a disease that refers to numerous clinical signs and symptoms resulting from an increase in pressure on the median nerve inside the carpal tunnel. The increased pressure compresses the median nerve, compromising its blood flow, resulting in the pain, numbness, and tingling characteristic of this disease. At present, it is the most widespread occupational health hazard in the industrial world. Billions of dollars are consumed each year in lost working time and in the diagnosis and treatment of this syndrome.
Intracarpal tunnel pressure is dynamic and influenced by numerous factors. Many of these factors have been studied previously, including disease, injury wrist position hand use compliance of the flexor retinaculum lumbrical muscles, externally applied force, and finger position. Not only does intracarpal tunnel pressure vary in response to these factors, but pressure dynamics also are determined by geometry of the carpal tunnel. Because of both the complex geometry and interaction among these factors, accurate measurement of intracarpal tunnel pressure remains difficult. In addition, pressure measurement is dependant on the type of measurement device used and whether introduction of the measurement device itself alters the pressure.
Active hand use produces the greatest range of pressures within the carpal tunnel. Most studies measuring intracarpal tunnel pressure during active hand use included patients with carpal tunnel syndrome (CTS). However, none of these studies quantified the hand use during pressure measurement. Because intracarpal tunnel pressure also is a function of location within the tunnel where pressure measurement is obtained, any characterization of the dynamics of intracarpal tunnel pressure should include a profile of pressure within the carpal canal. While others have identified the pressure profile that exists from proximal-to-distal within the carpal canal, only one of these included pressure measurements during active hand use. However, quantification of hand use was not reported.
Although the underlying cause of CTS is unknown, the treatment for CTS is well established. Non-operative treatments, including splinting, anti-inflammatory medications, and cortisone injections into the carpal tunnel, are often used initially to provide temporary relief of the symptoms. When non-operative treatments fail, the most effective treatment of CTS is surgical division of the flexor retinaculum. Surgical division of the flexor retinaculum causes a decrease in the pressure in the carpal tunnel allowing the return of normal blood flow to the median nerve, relieving the signs and symptoms of CTS. While various techniques exist for releasing the flexor retinaculum, the two most commonly used are open and endoscopic.
During an open release, a longitudinal incision is made through the skin in the palm of the hand and carried down through the subcutaneous fat, palmar fascia, palmaris brevis muscle, and finally through the flexor retinaculum. Once the flexor retinaculum is released, the skin is sutured and the wrist is frequently splinted until the wound heals. A typical surgery requires approximately 15 to 30 minutes and is performed as an outpatient procedure.
For an endoscopic release, various devices exist to perform incision of the flexor retinaculum. One device comprises a video endoscope and a hand piece that holds a disposable blade assembly. The device is inserted through a limited incision located in a wrist flexion crease. While viewing the deep side of the flexor retinaculum through a window located at the tip of the device, the blade is elevated to make the longitudinal incision while the device is withdrawn from the carpal tunnel. Next, the device is used to inspect the completeness of the incision through the flexor retinaculum and perform additional cutting if necessary. Once complete incision of the flexor retinaculum is achieved, the entry wound is sutured. The endoscopic release is performed as an outpatient procedure and requires approximately the same amount of time to perform as the open release.
Although complete surgical division of the flexor retinaculum is promoted as the standard of care in patients with CTS, there are a number of potential disadvantages associated with it, including:
(a) The arch formed by the carpal bones may be altered, affecting the functional biomechanics of the hand.
(b) The pulley effect created by the flexor retinaculum may be compromised and/or lost, allowing the digital flexor tendons and/or median nerve to sublux palmarwardly between the cut edges of the flexor retinaculum. Power grip and pinch are compromised until the flexor retinaculum heals adequately to re-establish the carpal tunnel as a competent pulley for the nine digital flexor tendons.
(c) Exposure of the cut edges of the flexor retinaculum permit scar tissue necessary for its healing in the lengthened position to be more abundant and therefore potentially creating greater post-operative morbidity, pain, and weakness.
(d) The length of time required for a patient to return to both their activities of daily living and work is affected by the trauma associated with a complete ligament division.
(e) The surgical techniques used require the expense of an operating room procedure rather than an office or clinic procedure.
(f) Following complete division of the flexor retinaculum, portions of the origins of the thenar and hypothenar muscle groups are unstable, causing pain and weakness of pinch and grip during the healing of the flexor retinaculum.
To avoid the potential disadvantages associated with current surgical techniques, an object of the present invention a method and apparatus that weakens the structural integrity of the flexor retinaculum without using a surgical incision or surgically dividing portions or all of the flexor retinaculum. At least some of these objectives will be met in the following description.